A mooring buoy can be illustrated as an example of use of a mooring rope. As shown in FIG. 8, upper ends of chains 101 are coupled to a mooring buoy B and an anchor AC is coupled to lower ends. The anchor AC is provided on a sea bottom and the mooring buoy B floats on a sea surface. In consideration of the rise and fall of a tide, a length of the chain 101 has a margin. In same cases, therefore, the chain 101 comes in contact with sand on a sea bottom or the like.
Although the chain 101 itself is formed of steel and has a high strength, it tends to be deteriorated by rust. If sand on a sea bottom intrudes into a portion between adjacent chains 101 so that it is often rubbed many times, wear of a corrosion layer proceeds quickly and is thus broken away. For this reason, the chain 101 is to be exchanged every two years or the like. Although an exchanging work is carried out in the water, the chain 101 has a great weight and a diver cannot perform the work and a working ship is required. As a result, a working cost is increased.
It is possible to solve the problem by using a rope in place of the chain 101. For example, the exchanging work in the water can be performed with a small load. When the rope is used in the sea, however, there is a problem in that sand and other fine impurities in the sea intrude into an inner part from the mesh of the rope and the rope is thus broken away in the early stage due to a friction between the impurities and a rope fiber.
The related art for preventing the friction of a rope or the like includes Patent Documents 1 to 3.
The Patent Document 1 discloses a rope-shaped thing in which a fiber structure obtained by twisting an organic fiber is set to be a core material portion and a surface thereof is coated with a thermoplastic resin.
Referring to the Patent Document 1, however, a coating configuration is unknown and it is characterized in that a resin to be used has thermoplasticity. Although the thermoplastic resin is convenient for coating formation, it has an unknown resistance in use for a long time with immersion in the sea.
The Patent Document 2 features a strand having a three-layer structure. An inner layer is a yarn obtained by collecting raw threads, and an outer intermediate layer thereof is a layer coated with a thermoplastic resin and an external layer on an outside thereof is a yarn obtained by twisting raw threads. In other words, the strand has a layer structure including an inner layer yarn, an intermediate coating layer and an outer layer yarn. For this reason, the strand is thickened and a rope obtained by knitting the thickened strand must be thick.
Moreover, the outer layer yarn exposed to an external surface of the strand is not protected by resin coating. In use in the sea, therefore, there is still a problem in that it is impossible to prevent wear from being caused by mixture of impurities in the sea, resulting in breakaway in the early stage.
Referring to the related art disclosed in the Patent Document 3, a cover is attached to an outer periphery of a rope, and the cover is configured from a rectangular cover body using a cloth-shaped member, a band-shaped non-slip mat, a flap and a surface fastener and is used with a proper part of the rope covered therewith.
However, the cover cannot prevent the intrusion of gravel on a sea bottom from intruding into an inner part of the rope. Thus, there is a great restriction to use in the sea.
Moreover, the cover is partially attached because the operability of the rope is damaged by attachment to a full length of the rope. For this reason, a wear resistance cannot be given to the full length of the rope.